ML20078K785
| ML20078K785 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 10/13/1983 |
| From: | Tucker H DUKE POWER CO. |
| To: | Adensam E, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8310190262 | |
| Download: ML20078K785 (3) | |
Text
s DUKE POWER GOMPANY P.O. Box 33180 CIIAHLOTTE. N.C. 28242 IIAL 11. TUCKER ret.EPHONE voos emmatoewt (704) 373-4531 October 13, 1983 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention:
Ms. E. G. Adensam, Chief Licensing Branch No. 4 Re: Catawba Nuclear Station Docket Nos. 50-413 and 50-414
Dear Mr. Denton:
Section 7.4.2.4 of Supplement 1 to the Catawba Safety Evaluation Report discusses Open Item 12, Loss of Both RHR Trains Resulting from a Single Instrument Bus Failure. Therein the Staff requested that an analysis be provided to confirm that sufficient time exists to reestablish decay heat removal if the RHR system is inadvertently isolated as a result of a loss of an instrument bus.
Consistent with the procedure for loss of RHR (AP/1/A/5500/19), the operator would sequentially attempt to restore cooling by three methods following loss of both RHR trains:
(1) Restore at least one RHR train to operation.
(2) Provide decay heat removal via the steam generators: forced circulation or natural circulation with steam dump to either the condenser or the atmosphere.
(3) Provide decay heat removal via the chemical and volume control system.
The analyses, a description of which is attached, shows that under very conserva-tive assumptions, at least an hour is available for operator actions. Thus, adequate time is available for the operater to take the necessary actions to reestablish residual heat removal, as outlined above.
Very truly yours, d k' e v
Hal B. Tucker ROS/php Attachment 0[
0 0310190262 831013 PDR ADOCK 05000413 I
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Mr. Harold R. Denton, Director October 13, 1983 Page 2 1
cc:
Mr. James P. O'Reilly, Regional Administratar U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30303 NRC Resident Inspector Catawba Nuclear Station Mr. Robert Guild, Esq.
Attorney-at-Law P. O. Box 12097 Charleston, South Carolina 29412 Palmetto Alliance 2135 Devine Street Columbia, South Carolina 29205 Mr. Jesse L. Riley Carolina Environmental Study Group 854 Henley Place Charlotte, North Carolina 28207 4
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Description of Analysis and Results The RHR system may be placed in service as early as four hours after reactor shutdown when the RCS temperature has been reduced to 350*F or less. A pressurizer steam bubble is maintained prior to this time and would be collapsed
-only near the end of cooldown when RCS temperature is low (i.e., 160*F or less).
A low temperature overpressure protection (LTOP) system which employs the pressurizer power operated relief valves (PORVs) limits reactor coolant system (RCS) pressure.
This system is enabled on decreasing RCS temperature. The temperature setpoint (presently 300*F) is selected such that the LTOP pressure relief setpoint (400 psig) is enabled before the limiting pressure for the RCS decreases below the PORV's normal pressure setpoint (2335 psig).
If a loss of both trains of RHR occurs with the LTOP system operational, the RCS temperature need only increase to saturation conditions for the LTOP pressure setpoint before steam formation may begin. As a minimum, the interval from the initiation of the loss of RHR transient to the beginning of steam formation is available for operator actions. At that time in the transient, there is still no immediately adverse or necessarily unacceptable consequences. Thus, actual time available for operator response is longer.
For analysis purposes only, 1) the RCS was assumed to be water solid, 2) the decay heat load was held constant at the value expected four hours post-shutdown (approximately 35.2 mw), and 3) RCS pressure was limited by LTOP operation.
These are very conservative assumptions which reduce operator action time.
A RETRAN02 model of the primary and secondary systems was utilized for the analysis. Steady state conditions were established with RHR in operation. The transient was initiated by isolating the RHR flowpath. Results were as follow.
The RCS temperature increases due to continued decay heat generation. With a water solid system, the pressure response is relatively rapid and RCS pressure increases to the point that the LTOP system permits. RCS pressure varies as the PORVs open and close.
The flowrate through the reactor initially decreases to about 50% and then recovers to approximately its original value as natural circulation becomes effective.
Eventually, after about 54.5 minutes, RCS temperature has increased sufficiently that the first steam formation begins at the reactor outlet during the RCS pressure minimum following a PORV opening cycle.
These bubbles collapse as pressure increases. Steam formation first occurs in the hot leg after about 61.8 minutes and they also collapse on increasing pressure.
Finally, after about 63.9 minutes, saturation conditions are maintained so that the steam bubbles do not collapse as pressure increases.
In conclusion, at least one hour is available for operator action, even under the very conservative assumptions of this analysis.